1. Field of the Invention
This invention relates to cleaning systems for electrostatographic printing machines, and more particularly for cleaning systems for a fuser or transfuse apparatus as employed in these machines. Even more particularly this invention relates to a method for refreshing a cleaner roll used to clean a fuser or transfuse subsystem as employed in a electrophotographic printing machine.
2. Description of the Prior Art
Electrophotographic marking is a well known and commonly used method of copying or printing original documents. Electrophotographic is typically performed by exposing a light image of an original document onto a substantially uniformly charged photoreceptor. In response to that light image the photoreceptor discharges so as to create an electrostatic latent image of the original document on the photoreceptor""s surface. Toner particles are then deposited onto the latent image so as to form a toner powder image. That toner powder image is then transferred from the photoreceptor, either directly or after one or more intermediate transfer steps, onto a marking substrate such as a sheet of paper. The transferred toner powder image is then fused to the marking substrate using heat and/or pressure. The surface of the photoreceptor is then cleaned of residual developing material and recharged in preparation for the creation of another image.
The foregoing generally describes a typical black and white electrophotographic marking machine. Electrophotographic marking can also produce color images by basically repeating the above process once for each color that makes the color image. For example, the charged photoconductive surface may be exposed to a light image which represents a first color, say cyan. The resultant electrostatic latent image can then be developed with cyan toner particles to produce a cyan image which is subsequently transferred to a marking substrate. The foregoing process can then be repeated for a second color, say magenta, then a third color, say yellow, and finally a fourth color, say black. Beneficially each color toner image is transferred to the marking substrate in superimposed registration so as to produce the desired composite toner powder image on the marking substrate.
The color printing process described above superimposes the various color toner powder images directly onto a marking substrate. Another electrophotographic color printing process uses an intermediate transfer member. In systems which use an intermediate transfer member successive toner images are transferred in superimposed registration from the photoreceptor onto the intermediate transfer member. Only after the composite toner image is formed on the intermediate transfer member is that image transferred and fused onto the marking substrate.
The most common developing materials are dry powder toners. Dry powder developers are typically comprised of not only toner particles but also of carrier granules. The toner particles triboelectrically adhere to the carrier granules until the toner particles are attracted onto the latent image. An alternative to dry powder developing materials are liquid developers. Liquid developers, also referred to as liquid inks, have a liquid carrier into which toner particles are dispersed. When developing with liquid developers both the toner particles and the liquid carrier are advanced into contact with the electrostatic latent image. The liquid carrier is then removed by blotting, evaporation, or by some other means, leaving the toner particles behind.
Intermediate transfer members can also be used in the fusing process. Intermediate transfer members which are used in fusing are referred to herein as transfusing members, and the combined processes of transferring and fusing is called transfusing. Transfusing is highly desirable in high image quality electrophotographic printing. Transfusing members are usually pinched between one or more contact rollers and a backup roller such that a fusing pressure is created between the nip of the backup roller and the transfusing member. During fusing a marking substrate moves between the backup roller and the transfusing member and heat is applied to the toner image. The combination of heat and pressure causes the toner image to transfer and fuse onto the marking substrate. Transfusing may be done without heat, but the resulting quality is usually inferior.
As referred to above, electrostatic printers are known in which a toner image is fused or fixed to a substrate to form a final document. The fusing can occur after transfer of the toner image to the substrate, or transfer and fusing can simultaneously occur in a transfuse process. In either arrangement the substrate is fed into a fusing nip where a combination of fusing members, such as fusing or transfuse belts or rollers, apply heat and pressure to the toner image and substrate to fix or fuse the toner image to the substrate. During the fusing process, toner particles from the toner image, and debris from the substrate can adhere to the fusing member. These toner particles and other debris and contaminants can transfer from the fusing member to subsequent documents in the machine resulting in print defects. In addition, the build up of toner particles can also decrease the operational life of the fusing member. Therefore it is preferred to be able to clean the fusing members to remove toner particles and other particulate debris, such as dirt and fiber, that can affect final print quality.
One prior cleaner for a fuser such as described in U.S. Pat. No. 3,649,992 employs a cleaning roller engaging the surface of a fuser roll to remove toner particles. A toner layer initially applied to the roller surface becomes partially molten and tacky due to heating from the hot fuser surface, and additional toner particles, paper debris, and other contaminants on the fusing system preferentially adhere to the cleaner roller during the cleaning process. As excess toner particles accumulate on the cleaner roller, the toner layer on the surface of the cleaner roller can become uneven, resulting in uneven cleaning of the fusing member. Also, as excessive contaminants are trapped by the tacky toner layer due to for example long printing runs, tackiness of the toner layer can be reduced and cleaning function relative to further ability to trap contaminants can begin to degrade. These problems can be reduced by adding sufficient additional toner layers onto the tacky cleaner to xe2x80x9crefreshxe2x80x9d the surface and restore tackiness and thus allow additional cleaning of contaminants.
For xe2x80x9crefreshingxe2x80x9d, a layer of toner can be periodically applied to the tacky cleaner surface in a variety of ways. For example, in a transfuse process a toner layer can be periodically developed and transferred to the transfusing member without engaging the final media substrate, and this refreshing layer of toner can then be made to adhesively transfer from the transfuse member to the tacky cleaner surface for refreshing the cleaner. Alternatively according to aspects of this patent application, for any type of fusing system toner layers can periodically be directly contact to, developed to, or transferred to the fusing member in a variety of other ways for refreshing the tacky cleaner via adhesive toner transfer to the cleaner from the fusing member. Further according to aspects of this patent application, toner layers can be more directly applied to the tacky member by various means such as by periodically engaging other surfaces to the tacky cleaner that have previously been covered with toner. For example, toner can be developed or otherwise previously applied to an additional roller or belt and the toner laden belt or roller can subsequently be engaged to the tacky cleaner member for refreshing the cleaner. Also, periodically, toner or like material can simply be substantially uniformly sprinkled onto the tacky cleaner.
These refreshing approaches can extend the ability of the tacky cleaner to clean contaminants for longer printing intervals. However, these approaches can not be continued indefinitely because eventually the toner layer on the cleaner roller can become excessively thick, and this can lead to back transfer to the fusing member of some fraction of the tacky toner layer, with resulting early failure of the cleaner. Thus a tacky cleaner requires maintenance to remove the excess toner in order to extend life and reliability of the cleaner.
In one alternative assembly (e.g. U.S. Pat. No. 4,607,947) the cleaner roller is formed of a hollow cylinder and apertures are provided in the cylinder to permit excess toner to be driven inward through the openings. Excess toner therefore is collected on the inside of the cylinder, extending the period between servicing or the life of the cleaner roller. However, the openings can result in gaps in the cleaning surface of the roller, requiring multiple cleaning cycles to completely clean the surface of the fusing member by the tacky cleaner. Therefore in a continuous printing system toner particles on the fusing member can continue to disrupt fusing, or be transferred to subsequent documents, before their removal. An object of the present invention is to eliminate the need for multiple cleaning cycles with a tacky cleaner while maintaining or extending life and reliability.
Another cleaning assembly for a fusing member is described in copending U.S. patent Ser. No. 09/464,134, now U.S. Pat. No. 8,223,016, filed Dec. 16, 1999 and assigned to the same assignee as the present application i.e. Xerox Corporation.
It is known to employ a sticky cleaner roll in an electrophotographic printer and refresh it by routinely (i.e. once per several hundreds copies) transferring uniformly developed solid toner image out the cleaner roll surface. Disadvantages of this method is that it consumes a large amount of fresh toner, and this can be wasteful and costly. Toners used for electrophotographic systems tend to require costly pigments, additives, charge-control agents, severe size classification and other special property requirements to enable processes such as image development and transfer, and these requirements typically add high cost to the toner.
Another objective of this invention is to reduce the cost and wastefulness associated with tacky cleaning and refreshing approaches. In one embodiment of this invention, a less wasteful approach is preferably used where the waste toner from other cleaners that would otherwise be discarded in the electrophotographic system is used for the tacky cleaner refreshment. In another possible embodiment, the refreshing xe2x80x9ctonerxe2x80x9d that is applied to the tacky cleaner member is lower cost material such as unclassified toner polymer particles or polymer layers rather than the toner used for the electrophotographic process. These less wasteful approaches can optionally be applied to any type of tacky cleaning system, such as existing perforated tube tacky cleaners, and these can be especially beneficial with the improved tacky cleaning systems described in this invention.
Other examples of cleaning systems employed in electrophotographic printers which relate to the technology described in this application are U.S. Pat. Nos. 3,649,992, 4,000,963, 4,013,400 and 4,607,947.
To achieve the advantages described herein in accordance with the purpose of the invention, the inventive features as embodied by the present invention include a method of refreshing a sticky cleaner member for a fusing system comprising the steps of: (I) precoating the cleaner member with a low cost polymer toner material prior to a printing operation; and (ii) removing contaminants from the sticky surface of the cleaner member.
In accordance with the features of the present invention lower cost raw polymer materials rather than higher cost toners are used in the electrophotographic system. Also the present invention employs a less wasteful approach by using the waste toner from other cleaning sub-systems such as photoreceptor cleaner in the electrophotographic system.
A refreshed cleaning member prior to being used to clean a fuser in an electrophotographic printer comprises a surface having substantially minimal contaminants thereon and a coating of a plastic toner material that can become tacky at the operating cleaner temperatures.